Lead Acid Batteries: Lead acid batteries are the most common type of energy storage.
All lead acid batteries are based on the same lead/sulphuric acid chemical reaction, however, they have evolved into different types – each designed for a specific need.
Smaller batteries look like big car batteries and contain several cells in tough plastic cases to give 6V or 12V with capacities up to ~ 200Ah. They are either flooded cell types: with a vent for gassing and topping-up with distilled water; or sealed/ gel types: with an immobilised electrolyte.
Larger battery banks are usually made up of flooded 2V cells ranging in capacity of ~100Ah to several thousand. Sealed types are also available. Some flooded cell batteries using tubular positive plates instead of flat plates have longer life.
Lithium Ion Batteries:
These have several advantages over conventional lead acid batteries:
Nickel Cadmium Batteries:
These are manufactured in many sizes. Sealed ones have very small capacities but are useful for self contained lights.
The larger ‘wet’ nicad is ideal for wind/solar energy storage. They require little maintenance; can be 100% discharged; left in any state of charge without damage; withstand overcharging; and withstand temperature extremes. However, they are several times the price of lead acid batteries. There are issues concerned with storage & recycling due to the toxic nature of Cadmium.
If discharged at a higher rate (by a higher current) then battery capacity is reduced considerably. The maximum charge/discharge current should be less than 10% of battery Ah capacity.
The capacity of the battery bank needed depends upon:
The one requiring largest capacity will dictate battery size.
This is measured in number of discharge/charge cycles rather than years. The more deeply the battery is discharged the lower the number of cycles it will last for. The percentage depth of discharge (DOD) of a battery means how much of the available power in the battery is used before recharge.
Overcharging a battery raises the temperature of the electrolyte, causing excessive gassing, loss of distilled water and eventually damage to the plates. Excessive discharge of a battery can also lead to permanent damage. If a battery is close to its fully discharged state it should be recharged immediately (eg. by using a generator & charger) – or if that is not possible all loads switched off until the battery can be charged.
Batteries need to be regularly boost charged and allowed to ‘gas’ freely for an hour or so. This equalises individual cell voltages within the battery and helps avoid electrolyte stratification.
No battery is 100% efficient. Energy is lost in storage, charging and discharging. With new cells, efficiencies of 90% can be expected, however this decreases with age, sulphation and stratification. To maximise efficiency, batteries should be kept at room temperature, and sized correctly for their purpose, both to minimise self discharge, and to prevent them being charged and discharged too rapidly.
The battery bank should be installed, preferably on its own, in a weather & frost protected, well ventilated shed or other enclosed area. Ideal temperature is ~ 20 ºC and should not be more than 43 ºC.
This is how much of the battery capacity is available (how full it is). The most convenient way of determining this is by measuring the battery voltage. Ideally for a battery that has been at rest for three hours (ie. neither being charged or discharged). Measurement should only be performed with an accurate hydrometer. The normal automotive type is not suitable. A hydrometer cannot be used with sealed or gel-cell batteries.
If you want any more information on battery storage, simply get in touch with our renewable energy experts. Call our team on 0118 984 1753, or leave your details on our contact us page and await a swift reply.
We install across Oxfordshire, Berkshire and in parts of Buckinghamshire, Wiltshire, Hampshire and Surrey. We ensure there is an accredited installer near you. get in touch now by entering your postcode below.
Dedicated Sales Team ready to work with you